This invention is generally directed to the etching of materials in integrated semiconductor products. It is particularly directed to an improved technique for etching patterns in materials which include silicides as components of an integrated circuit product.
In fabricating semiconductor products, materials such as titanium are sometimes combined with other materials such as silicon to form a resultant material of low resistivity. In the case of titanium and silicon, the titanium may be combined with silicon to form titanium silicide (TiSi.sub.2) which may have a resistance which is lower than the resistance of silicon by a factor of twenty. This low resistivity material is known to be useful in a variety of applications, such as the formation of relatively long word lines in semiconductor memories.
A known problem with the use of silicides (which, as used herein, means silicide compounds) in semiconductor products is the difficulty with which silicide is etched. Where the silicide overlies a layer of polysilicon, it has been difficult to etch through the silicide and through the polysilicon without undercutting the polysilicon material or etching the dielectric layer. Such difficulty presumably arises because of the tendency of the etchant to remove polysilicon faster than it removes the silicide.
An associated problem is that of obtaining an anisotropic etch, i.e. an etch ideally in one direction only, such as required to obtain apertures having substantially vertical sidewalls. Existing literature in the semiconductor field purports to obtain anisotropic etching in polysilicon using plasma etching techniques and certain gases. See, for example, U.S. Pat. Nos. 4,208,241 and 4,211,601. However, these existing techniques do not provide anisotropic etching of silicides, at least not of the character which is required for high volume production.
Another difficulty with existing etching techniques is their tendency to etch deeper than desired so as to remove portions of an underlying layer which is intended to be left intact. When the underlying layer is a gate oxide, removal of the gate oxide leads to difficulties with which those skilled in the art are familiar.
Accordingly, it is an object of the invention to provide an improved technique for etching patterns in materials which include silicides as components of an integrated circuit product.
It is another object of the invention to provide a method for etching highly anisotropic patterns into and through polysilicon layers which underlie a material containing silicide.
It is another object of the invention to provide such anisotropic etching and yet avoid any substantial removal of oxide which may underlie the materials to be etched.